TANGRA designed and executed ventilation, heating and air conditioning systems in the newest office building of UniCredit Bulbank

At the end of 2015 TANGRA’s team completed the ventilation, heating and air conditioning installations in new administrative building, located near the tunnel at the “Pencho Slaveykov” blvd. in Sofia. It is the second stage of a private investment, intended for a business building to meet the needs of “UniCredit Bulbank”. The total floor area of the two buildings is 18 500 sq.m.

The new building is multi-functional and it accommodates offices, a restaurant, a kitchen for the restaurant, a fitness center, a commercial shop and an underground parking. The people, employed in the building and using its offices on a daily basis exceed one thousand. The stylish new facade corresponds to the exiting building, which was completed in 2009 (stage I) and establishes a completely new appearance of the entire area. Thanks to the excellent performance and satisfying the occupant’s needs in the first stage, the specialists from TANGRA were invited to design and were awarded the contract for the implementation of the HVAC installations in the second stage of the project.

The challenges and requirements, inherent to the micro-climate systems of such buildings are numerous, and the large number of inhabitants, the computer equipment used and the extensively glazed facades, require precise solutions. From the very first moment of preparation of the detailed design, the main concept for this project was to implement installations with maximum energy efficiency, ensuring the necessary comfort in the premises. All the efforts were focused on the use of energy recovery systems. The main advantage of this solution was the maximum degree of autonomy, reliable operation and the achievement of a micro-climate, meeting the regulatory requirements.

A Hitachi Chiller and additional heat supply from a district heating substation were employed for the first building. An even more contemporary solution was selected for the second building. Therefore TANGRA’s experts chose a three-pipe system with direct evaporation units and variable quantity of the cooling agent – Hitachi VRF (variable refrigerant flow). 

One of investor’s requirements was to ensure simultaneous heating of certain premises and cooling in other, adjacent premises. This was another reason to choose the VRF system. These air conditioning machines transfer the discharged heat between the internal units, reducing the energy, used by the external units by 10-15% during the transitive periods and in winter.

The frequency invertor control of the air conditioning, ventilation systems and the heating follows the thermal needs of the building, further reducing the electricity consumption.

The high transformation ratio of the air conditioning units Hitachi VRF, COP 4,04 and 3,62 ЕЕR shows how efficient these systems are. In standard calculation conditions as per EN 14511, for 1 kW of consumed electricity the system produces approximately 4 kW of heating energy during winter and approximately 3.5 kW cooling energy in summer.

Ventilation is another significant factor, contributing to the well-being of the users. Modern buildings are not expected to be ventilated by opening windows. This is an energy inefficient method, noisy and unhealthy in the polluted urban conditions. On the other hand, fresh air is vital for people’s health and working capacity.

In order to provide fresh air, the ventilation systems were designed and constructed in conformity with the regulatory requirements of Class “A” installations. The installed ventilation air handling units for supply of fresh and exhaust of pollutant air are of the TANGRA AHU ROT and TANGRA EVB HiE series. They are produced with high efficiency counterflow plate heat exchangers or rotary regenerative wheel heat exchangers with efficiency between 72 and 88%, which ensures the following advantages:

• Guaranteed highest energy efficiency of the HVAC systems.
• Reduced capital investment in a heating and cooling center.
• Reduced carbon footprint of the building. 

TANGRA’s air handling units are designed and programmed to ensure operation in Free cooling mode. This means the use of external air, as the cooling media in the interval 16° to 24°С. In Sofia, this means almost 2000 hours per year. In this period, the air handling units receive free “help” from the environment and consume much less energy for cooling the fresh air.

The high efficiency heat recovery ventilation systems are designed to ensure low operating costs, not only through their heat exchanger sections, but also through the fans sections. The air handling units and heat recovery units are produced with centrifugal fans with backward curved wheels and frequency inverter control. This enables the transportation of air with lower power consumption, compared to the belt driven fans. At the same time this ensures secure operation of the system, by eliminating any possibility of failure due to a broken belt. Another significant feature is that the frequency inverters TANGRA FI enable the change of the rotations per minute, i.e. the flow rates of the transported are adjusted, according to the inhabitants of the building.

In conclusion, it should be noted that due to the precise architectural and construction design of “Stroyconsult 999” OOD and the excellent coordination with the main contractor – “Comfort” OOD, we managed to execute a successfully one energy efficient project. The tenant of the building uses all the office floors, the restaurant, fitness centre and grocery and household store. The excessively cold days in January (below -20оС) proved an important test of the system operation in extreme conditions. The HVAC design solution and the properly selected high efficiency air conditioning units Hitachi VRF and air handling units TANGRA AHU ensure low energy operating costs.